1. Field of the Invention
The present invention relates to a method of separating isotopes. More particularly, the invention relates to a method of separating a specific isotope from a mixture of isotopes by first irradiating the isotope mixture with a highly monochromatic laser light that resonates only with the energy level of the specific isotope so as to increase its chemical activity and then bombarding said specific isotope with a molecule containing highly reactive atoms so as to form a compound rich in the specific isotope.
2. Description of the Prior Art
For separation of isotopes by laser, it is important to fix and recover the atoms excited by the laser. The conventional technique for attaining this object is to ionize only the excited atoms with a light having a suitable wavelength and to collect them in an electric or magnetic field. This technique, generally referred to as the photoionization method, requires a laser of high power (for multiple-photon ionization) or more than one laser (for multi-stage ionization). The photoionization method is hereunder described in detail with particular reference to the separation of uranium, lithium, calcium, rubidium or lanthanum isotopes.
A mixture of isotopes is irradiated with a laser light that resonates only with the energy level of the target isotope. The target isotope absorbs the laser light and is subsequently irradiated with a laser light from the same or a different source. Upon absorbing the second laser light, ions are generated by photo-ionization of the target isotope and subsequently recovered by physical means. However, in the conventional method, exchange of electric charges occurs between the ions of the target isotope and the other neutral isotopes, and as a result, the number of ions derived from the target isotope is decreased whereas the number of ions derived from the unwanted isotopes is increased, and this leads to lower yields and separation factors.
Furthermore, the cross section of an atom for ionization is smaller than that for excitation by a factor of 10.sup.3 to 10.sup.4. Therefore, there is a significant difference in transition probability between excitation from the ground state to the first stage of excitation and from the first stage to the second stage of excitation due to ionization. In order to achieve efficient two-stage ionization, the light source for photoionization must have an intensity 10.sup.3 to 10.sup.4 times greater than that of the laser light for the first stage of excitation (selective excitation). Ionization involves an excitation to the continuous energy state and requires a laser of high power although this does not need high monochromaticity.
In three-stage photoionization, three photons having different frequencies are used: the first photon has a frequency that selectively excites the target isotope, the second photon has a frequency that boosts the same isotope to an upper excited state, and the third photon has a frequency high enought to ionize said excited isotope. Therefore, three visible lasers are required, and the overall system including pumping sources and control devices becomes correspondingly complicated.
In the conventional method of separating barium isotopes, their mixture is irradiated with a laser light and by deflecting the orbit of a specific isotope through absorption of the laser light, said isotope can be directly recovered in the electrically neutral state. However, the deflection of the orbit of the specific isotope is so small that the neutral atoms cannot be recovered in high yield.